Magnetic scanning circuits for cathode ray tubes



1959 P. KIRKHAM ET AL 2,899,578

MAGNETIC SCANNING CIRCUITS FOR CATHODE RAY TUBES Filed May 5. 1955 Inventor e i er /f/'r/fiam Raymond G. R 6 06/); son

Attorneys United States Patent MAGNETIC SCANNlNG CIRCUITS FOR CATHODE RAY TUBES Peter Kirkham and Raymond Gray Cambridge, England, assignors to Pye Limited, Cambridge, England, a British company Rippon Robinson,

The present invention relates to magnetic scanning circuits for cathode-ray tubes and the like and more particularly to means for controlling the amplitude of the waveform deflecting the cathode-ray beam.

A conventional arrangement for achieving the magnetic deflection of a cathode-ray beam is to supply energy to two or more coils positioned around the neck of the tube. Each coil is generally of the saddle type and comprises two limbs lying parallel to the axis of the tube neck, which limbs produce the field causing the deflection of the electron beam, and two sets of cross limbs which merely act as electrical conductors.

A form of amplitude control commonly employed with such deflector coils consists of a variable inductance in series with the deflector coils. Such an arrangement suffers from the disadvantage that oscillations set up in the control coil are impressed on the deflector coils and appear on the trace as a velocity modulation. This necessitates critical damping of the control coil which makes the method ineflicient, as energy in the damping circuit is not recoverable by an efliciency diode.

It is an object of the present invention to provide a means for controlling the amplitude of the deflecting Waveform which overcomes these disadvantages.

To this end the present invention comprises a deflector coil, for deflecting the electron beam of a cathode-ray tube or the like, in combination with means provided for varying the inductance of a portion of the coil, which portion does not normally serve to cause the desired deflection of the electron beam.

The portion of the coil which does not normally serve to cause the desired deflection of the electron beam may comprise the end turns of the deflector coil which extend transversely to the axis of the tube neck, and a variation in the inductance of these end turns will therefore be equivalent to the action of a separate series control coil. Furthermore, the variable inductance is now an integral part of the deflector coil and the ringing caused by the use of an auxiliary control is not experienced.

The invention also consists in a deflector coil assembly, comprising a plurality of coils adapted to surround the neck of a cathode-ray tube or the like, each coil having two limbs adapted to extend parallel to the longitudinal axis of the tube neck and two cross limbs extending transversely of the longitudinal axis of the tube neck and joining the first two mentioned limbs, in which means are associated with at least one of the cross limbs for varying the inductance of said cross limb or limbs.

The means for varying the inductance preferably comprises a magnetic path surrounding the appropriate part of the coil with provision for varying the reluctance of the path i.e. by providing a variable air gap. The magnetic path should consist of laminated magnetic material such as ferrite, or of a powdered iron material having a low conductivity, so as to avoid loss of power by eddy currents.

In order that the invention may be more fully understood, reference will now be made to the accompanying drawings, in which:

Figure 1 shows a side view of a deflector coil assembly according to the invention.

Figure 2 shows an end view of the deflector coil assembly in Figure 1, and

Figure 3 is an explanatory diagram showing the equivalent inductances of the deflector coil assembly in Figures l and 2.

In the drawings, a deflector coil assembly adapted to surround the neck of a cathode-ray tube comprises four saddle type deflector coils 1, 2, 3 and 4. The coils 1 and 2 consist of two limbs 1a, 1b and 2a, 2b respectively, adapted to extend parallel to the longitudinal axis of the neck of the cathode-ray tube, which limbs cause the deflection of the beam, and two cross limbs 1c, 1d and 2c, 2d, respectively which comprise the connection or end turns. According to the invention, the end turns 10 of the coil 1 are surrounded by means for varying the inductance of the end turns comprising members 5 and 6 made of a ferro-magnetic material. The member 5 which is U-shaped is arranged around the turns 10, whilst the member 6 is substantially flat and extends across, but is generally spaced from the ends of the arms of the U. This latter member is carried by a screw 7, and nut 7a, from a bracket 8 secured to the frame 9 of the deflector coil assembly. The reluctance of the magnetic path through the members 5 and 6 can be varied by adjustment of the air gap between the member 6 and the ends of the arms of the U-shaped member 5 by rotating the nut 7a on the screw 7, which in turn varies the inductance of the end turn 10 of the coil 1, which is in effect an adjustment of the inductance in series with the deflector coils. To avoid loss of power by eddy currents induced in the members 5 and 6 these are made of a material having a low conductivity such as ferrites, or are lami nated.

Figure 3 shows the equivalent circuit of the inductances forming deflector coils 1 and 2 of the assembly in Figures 1 and 2.

Whilst a particular embodiment has been described it will be understood that various modifications may be made without departing from the scope of the invention. For example the magnetic member providing the variable magnetic path may be made in any convenient form. If desired more than one device for varying the inductance can be as associated with one deflector coil, or with the deflector coil assembly.

We claim:

1. A deflector coil for deflecting the electron beam of a cathode-ray tube or the like in combination with an adjustable magnetic member for varying the inductance of the coil and means for supporting said adjustable magnetic member so that it extends around a portion of the coil, which portion does not normally serve to cause the desired deflection of the electron beam.

2. Apparatus as claimed in claim 1, in which the deflector coil is of the saddle type, and the adjustable magnetic member is arranged around the end turns of the deflector coil which extend transversely to the axis of the neck of the cathode-ray tube or the like when the coil is in position around said neck.

3. A deflector coil assembly, comprising a plurality of coils adapted to surround the neck of a cathode-ray tube or the like, each coil having two limbs adapted to extend parallel to the longitudinal axis of the tube neck and two cross limbs extending transversely of the longitudinal axis of the tube neck and joining the two first mentioned limbs, and an adjustable member defining a magnetic path arranged around at least one of the cross limbs and Patented Aug. 11, 1959 aelhdih means f r varying the uc an e of i pa h in order to vary the inductance of said cross limb.

4. Apparatus as claimed in claim 3, in which the adihsteble member d fin n th ma e te pa h comp i e a; U-shaped member arranged around a cross limb, and a hhstah al y fla member xt din e essw epeee from the ends of the arms of the U-shapcd member, the e r. m mb be di teb in. pos ti n, o va y t air gap between itself and the ends of the arms oi the sher d, membe p ar us a ele me n e hh 4, n. whi h h u stantially flat member is carried from a bracket secured he hem Qt he e e or eei a s mbly y eans of screw d i e the s hee between said member. and h ehds ef h arms of he U- haped memb be n ad usted b ani u at 9i s id erew de i e:

6,- Apper i s as c i ed h' lah bh 3 in h h the adi s eble memb r i in de o am e heshe e m riel- 7 -Ari r t as im n e h 3 l wh eh th d u ab e m mbe s ma e ef P e e r h mete e .z

A d fle e e l ass mb ordefl et hs th e ctron ea o e a ea de eemp is h a l ast ne defle r e l pted t eh euh th h e s i sai ceth d e de d an, a iustahle de ee defih h e m he ie Pa h ra ed excee a p rti n at he so l w eh deee h herm ll er i eeuse h e red 1 flee ieh. hi the e eet h be n sa de ee eemp sih e U s e ed mem e ar e ereuhd aid por on a d a brid e mem r ext n i 1 55, hat paced te t the ends i he ar s o th U-shered hie e and .ih ens er ad st e e 9t said memb r t9 varyhe ai can betw en ai m mbers, hd h e h re u t hee a said he e ie pa and th hd eteh e e sai c i hr e e u as l m i elehh 8, in whieh t e adiheteh e d e s a e of lam nat d ie heti m ter el- .lQ- ppara us as e a tmed in claim, n wh eh th adjustab e d ee s m d Qt Pewde ed hen m r a '11- A defl te l a semb for e eet h th l ehen am o e ath de-ra e iee eerhn s h t eas one deflector coil adapted to surround the neck 0t said eathed y de ic and. er; adius h e dev ee defin a m h t e p th r a d e ehhs n rt en hi the co l which does not normally 'serve to cause the desired defleet eh e he e eh he th. sa de iee e inpr sin a u h re member r anged e ehh said, porti n, and a rid e me b x n heroe but epa etl f t e n so the a m o he J-sh ee mem er, a ppor ing bracket, and a screw member; tor supporting said bridge member m d b e man pula ion f sa se ew b varying the Po i e of sa d br ge mem elative to the U-"shaped member and so varying the gap between said members and hence the reluctance of said magnetic path and the inductance of said coil.

A de c r eeil a em y er d ee ih t e elec-. tre b of e a h de-my ie eempr sing a P 1 ae ae e rality of deflector coils adapted to surround the neck of said cathode-ray device, each coil having two limbs adapted to extend parallel to the longitudinal axis of said neck and two cross limbs extending transversely of the longitudinal axis of said neck and joining the two first mentioned limbs and an adjustable device defining a magnetic path arranged around one of the cross limbs, said device comprising a U-shaped member arranged around said cross limb and a bridge member extending across but spaced from the ends of the arms of the U-shaped member and means for adjusting one of said members to vary the air gap between said members and hence the reluctance of said magnetic path and the inductance of said coil.

13. A deflector coil assembly for, deflecting the electron beam of a cathode-ray device, comprising a plurality of deflector coils adapted to surround the neck of said cathode-ray device, each coil having two limbs adapted to extend parallel to the longitudinal axis of said neck and two cross limbs extending transversely of the longitudinal axis of said neck and joining the two first mentioned limbs and an adjustable device defining a magnetic path arranged around one of the cross limbs, said device comprising a U-shaped member arranged around said cross limb and a bridge member extending across but spaced from the ends of the arms of the U-shaped member, a supporting bracket, and a screw member for supporting said bridge member from said bracket, manipulation of said screw member varying the position of said bridge member relative to the U-sliaped member and so varying the air gap, between said members and hence the reluctance of said magnetic path and the inductance of said coil.

14. A deflector coil assembly for deflecting the electron beam of a cathode-ray tube, comprising a. plurality of coils adapted to surround the neck of said cathoderaytube, an adjustable device of magnetic material defining a magnetic path arranged around a portion of one of the coils, said device including means for varying the reluctance of said magnetic path and hence the inductance of the coil about which said device is arranged in such a way that uniformity of the active magnetic deflecting field is not substantially impaired.

Ref rehee Q ted n. he fi e o his p en UNITED STATES PATENTS 

